Organophosphate pesticides (OP) pose risks to health and the environment, and monitoring them is an urgent task. Development of a method for their determination in water and food. A simple photometric method for the determination of some OPs was demonstrated. Ag-EDTA-Zr and Au-EDTA-Zr nanoparticles were synthesized and were applied for the determination of some OPs (dimethoate, chlorpyrifos, and diazinon). It was demonstrated that silver nanoparticles provide more sensitivity in comparison to gold nanoparticles. As a result, Ag-EDTA-Zr nanoparticles were further applied for the determination of these pesticides in tomatoes. The lowest detectable concentrations for dimethoate, diazinon, and chlorpyrifos in water reached 0.1 (SD 0.082), 0.4 (SD 0.075), and 0.4 mg/L (SD 0.088), respectively, whereas in tomato the lowest detectable concentrations for these pesticides were 0.5 (SD 0.789), 2 (SD 0.085), and 0.5 mg/L (SD 0.088). The sensitivity of detection in tomatoes is lower than in water; however, these concentrations are comparable with allowable concentrations of OP pesticides. A novel approach for quantitative detection of OPs was developed. Ag-EDTA-Zr and Au-EDTA-Zr nanocomposites interact with these pesticides, and, as a result, optical changes of these nanoparticles take place. These changes correlate with the concentration of pesticides.